The present invention relates to a silver halide photographic photosensitive material and more particularly to a roomlight silver halide photographic photosensitive material which has suitable reversal characteristics and is superior in safety against safelight (white fluorescent lamp from which ultraviolet ray has been excluded).
Recently, improvement of efficiency in the field of printing has been demanded due to complexity of step of reversing operation resulting from complexity of prints and development of scanner. Therefore, photographic films much lowered in sensitivity as compared with conventional films for reversing have been developed and have begun to be used as films which can be handled under roomlight (under white fluorescent lamp from which ultraviolet ray has been removed), namely, as roomlight photosensitive materials.
In general, emulsions of such ultra-low sensitivity as can be utilized as roomlight photosensitive materials are obtained by further adding a dye for lowering the inherent sensitivity to a silver halide photographic emulsion which has been desensitized with an inorganic desensitizer such as rhodium salt or an organic desensitizer such as pinakryptol yellow alone or with combination of these desensitizers.
On the other hand, in reversing step of printing plate making process, there are often carried out not only the negative-positive conversion by simple one sheet contact printing reversal, but also adjustment of line width of letter or adjustment of area of dots of dot image by control of exposure and besides, high-degree image conversion operation such as removal of letter.
Removed letter means the portion which is omitted in the form of letter or line in dot images such as those of photographic originals in printed matters (namely, the portion which does not receive ink). Specifically, as shown in the drawing attached hereto, dot original (E) stuck on base (D) and letter.multidot.line original (B) stuck on base (A) are put together and reversal photosensitive material (F) is subjected to contact exposure through them as original. In some case, several sheets of film (C) may be inserted as a mask between the dot original and the letter.multidot.line original.
Therefore, even if an exposure enough to convert the dot original to 1:1 (namely, to convert dots of x% to (100-x)%) is applied, the letter line image becomes unsharp and width of line becomes thinner than that of the original because of the exposure through several sheets of spacers. This is fatal in the step of removal of letter.
However, if, as mentioned above, a dye which reduces inherent sensitivity is added to emulsion layer in order to lower sensitivity of silver halide photographic emulsion to such extent as it can be utilized as a roomlight photosensitive material, there are the defects that functions to adjust the area of dots of dot image and width of letter line by control of exposure are lost and besides, exposure required for conversion of dot original in 1:1 markedly increases and so line width of removed letter becomes thinner and in the worst case, thin original is broken.
For solving these defects, there has been proposed to contain a dye to lower the inherent sensitivity in a non-photosensitive hydrophilic colloid layer provided above silver halide emulsion layer, namely, at a position remoter than the emulsion layer from support as in Japanese Patent Kokai (Laid-Open) Nos. 59-193447, 61-198148 and 61-240235. However, according to this method, fixation of the dye in the non-photosensitive layer by mordant is not sufficient and it is unavoidable that line width of removed letter becomes thinner as mentioned above due to penetration of the dye into the silver halide photosensitive emulsion layer.
On the other hand, however, when no dye which lowers the inherent sensitivity is contained in the silver halide emulsion layer, there occurs the problem that so-called fringes are formed due to blur of image caused by irradiation.
Therefore, there have been desired roomlight reversal photosensitive materials which are superior in adjustability of line width of letter and area ratio of dots by control of exposure and are free from formation of fringes.
There is the another problem that if amount of the dye used in roomlight photosensitive materials is restricted, safety against white fluorescent lamp from which ultraviolet ray has been excluded which is used as safelight is damaged.